The natural hormone, 1α,25-dihydroxyvitamin D3 and its analog in the ergosterol series, i.e. 1α,25-dihydroxyvitamin D2 are known to be highly potent regulators of calcium homeostasis in animals and humans, and more recently their activity in cellular differentiation has been established, Ostrem et al., Proc. Natl. Acad. Sci. USA, 84, 2610 (1987). Many structural analogs of these metabolites have been prepared and tested, including 1α-hydroxyvitamin D3, 1α-hydroxyvitamin D2, various side chain homologated vitamins and fluorinated analogs. Some of these compounds exhibit an interesting separation of activities in cell differentiation and calcium regulation. This difference in activity may be useful in the treatment of a variety of diseases such as renal osteodystrophy, vitamin D-resistant rickets, osteoporosis, psoriasis, and certain malignancies.
Recently, a new class of vitamin D analogs has been discovered, i.e. the so called 19-nor-vitamin D compounds, which are characterized by the replacement of the A-ring exocyclic methylene group (carbon 19), typical of the vitamin D system, by two hydrogen atoms. Biological testing of such 19-nor-analogs (e.g., 1α,25-dihydroxy-19-nor-vitamin D3) revealed a selective activity profile with high potency in inducing cellular differentiation, and very low calcium mobilizing activity. Thus, these compounds are potentially useful as therapeutic agents for the treatment of malignancies, or the treatment of various skin disorders. Two different methods of synthesis of such 19-nor-vitamin D analogs have been described [Perlman et al., Tetrahedron Lett. 31, 1823 (1990); Perlman et al., Tetrahedron Lett. 32, 7663 (1991), and DeLuca et al., U.S. Pat. No. 5,086,191)].
In U.S. Pat. No. 4,666,634, 2β-hydroxy and alkoxy (e.g., ED-71) analogs of 1α,25-dihydroxyvitamin D3 have been described and examined by Chugai group as potential drugs for osteoporosis and as antitumor agents. See also Okano et al., Biochem. Biophys. Res. Commun. 163, 1444 (1989). Other 2-substituted (with hydroxyalkyl, e.g., ED-120, and fluoroalkyl groups) A-ring analogs of 1α,25-dihydroxyvitamin D3 have also been prepared and tested (Miyamoto et al., Chem. Pharm. Bull. 41, 1111 (1993); Nishii et al., Osteoporosis Int. Suppl. 1, 190 (1993); Posner et al., J. Org. Chem. 59, 7855 (1994), and J. Org. Chem. 60, 4617 (1995). Recently, similar analogs of 1α,25-dihydroxy-19-norvitamin D3 have also been synthesized, i.e., compounds substituted at 2-position with hydroxy or alkoxy groups (DeLuca et al., U.S. Pat. No. 5,536,713), which exhibit interesting and selective activity profiles. All these studies indicate that binding sites in vitamin D receptors can accommodate different substituents at C-2 in the synthesized vitamin D analogs.
Recently analogs which are characterized by the transposition of the ring A exocyclic methylene group, present in the normal vitamin D skeleton, from carbon 10 (C-10) to carbon 2 (C-2), i.e., 2-methylene-19-nor-vitamin D compounds, were synthesized and tested. Molecular mechanics studies indicate that such molecular modification does not change substantially the conformation of the cyclohexanediol ring A. However, introduction of the 2-methylene group into 19-nor-vitamin. D carbon skeleton changes the character of its (1α- and 3β-) A-ring hydroxyls. They are both now in the allylic positions, similarly, as 1α-hydroxy group (crucial for biological activity) in the molecule of the natural hormone, 1α,25-(OH)2D3. These analogs have exhibited similar rate of binding to the receptor as 1α,25-dihydroxyvitamin D3 and were also characterized by high cell differentiation activity. These compounds were characterized by little, if any intestinal calcium transport activity, as compared to that of 1α,25-dihydroxyvitamin D3, while exhibiting relatively high activity, as compared to that of 1α,25-dihydroxyvitamin D3 in their ability to mobilize calcium from bone.
More than ten years ago an interesting 1α-hydroxyvitamin D analog was synthesized, namely, 1α-hydroxy-20-methyl-pregnacalciferol (also sometimes referred to as 1α-hydroxy-homopregnacalciferol) which was essentially devoid of calcemic activity, showed some HL-60 cell differentiation ability but unexpectedly exhibited comparable binding to the receptor as 1α,25-dihydroxyvitamin D3 [Lau, W. F. (1986) Ph.D. Thesis, University of Wisconsin-Madison]. In a continuing effort to explore the 19-nor class of pharmacologically important vitamin D compounds, a 1α-hydroxy-19-nor-vitamin D analog, which is characterized by the presence of methylene substituent at the carbon 2 (C-2) and 17β-isopropyl side chain has now been synthesized and tested.